The experiments proposed below are designed to examine development in the olfactory bulb and its principal synaptic targets, the anterior olfactory nucleus and primary olfactory cortex. The olfactory system has been chosen for several reasons. First, it is highly organized, facilitating quantitative examinations of early development and making subtle alterations relatively easy to discern. Many interesting forms of early plasticity have been demonstrated in the system, including inductive tissue interactions and substantial sensitivity to early stimutation. Indeed early unilateral odor deprivation has been repeatedly demonstrated to result in some of the largest experience-induced changes observed in the central nervous system. As a result the region affords considerable potential for examinations of the mechanisms by which environmental factors help to specify early growth. Two groups of experiments are proposed. The first continues our quantitative examination of early olfactory bulb development in the rat which emphasizes studies of how alterations in functional activity affect bulb growth. Specifically, we will examine: patterns of protein synthesis both in normally developing and deprived bulbs to examine the early cell biology of the olfactory system changes in the development of bulb glia populations. Another set of studies examines early bulb growth in the gray, short-tailed opossum Monodelphis domestics. Monodelphis pups are born in a very immature state, and are quite accessible to early experimental manipulation allowing in depth examinations of early tissue interactions. Specific experiments include: examinations of early functional deprivation to gauge how activity influences early growth. assessment of the effects of bulb removal on the development of higher order olfactory structures. In summary, the proposed research will explore early developmental processes such as the instructive interactions which occur between tissues and the role of afferent activity in growth and differentiation.